The subject matter disclosed herein relates generally to a rotor structure of an electric machine such as a generator. More particularly, the invention relates to a laminated rotor structure for an electric machine, and a balancing member structure for the same.
Generators typically include a stator and a rotor, the rotor rotating about a longitudinal axis within the stator to convert mechanical energy into electrical energy. The stator typically includes windings from which electrical power is output.
The rotor includes axially extending slots about the circumference of the rotor body, which extend lengthwise along the rotor body. These slots contain stacked coils which form the rotor field windings for carrying current. The rotor field windings are supported in place against centrifugal forces by using one of a number of different systems including, e.g., coil wedges which bear against the slot surfaces. The regions of the coils which extend beyond the ends of the rotor body are referred to as end windings, and are retained against centrifugal forces by retaining rings. The portion of the rotor shaft forging which is located under the rotor end windings is referred to as the spindle.
Rotors may be formed from a solid single forging of high strength iron or steel, to provide the rotor with the required bending stiffness to support the rotor statically and to transmit torque from the rotor to a drive flange of the generator for successful operation of a large, high speed generator. These solid single-forging rotors are expensive to produce, and limited production capacity may result in long lead times for ordering and manufacturing.
Laminated rotor bodies have been used in some electric machines such as generators and motors to alleviate the expense and lead time associated with solid steel rotors. These laminated rotor bodies comprise laminations placed on, or attached to, a single steel shaft, such that the shaft provides the required bending stiffness for the rotor. Laminated rotor bodies have also been used in electric machines in which the stack of laminations is held in compression by a series of rods that pass through holes in the periphery of the laminations. Relative to forged rotors, laminated rotors may be more prone to deformities as a result of fault torques and radial runoff, and therefore may require more frequent and/or more extensive rebalancing throughout the lifespan of the rotor.